The present invention is in the field of torquers, and more particularly relates to solenoid torquers particularly useful in inertial instrumentation.
The development and practical application of tactical two degree of freedom (TDF) inertial instruments has been substantially limited due to deficiencies in the known forms of rotor torquing systems. Consequently, TDF instruments, such as the dynamically tuned gyro (DTG), have been characterized by a relatively high cost and low angular rate capability.
One prior art system utilizes permanent magnet (PM) torquers. However, such systems have thermal sensitivities which typically are so large as to require first order scale factor correction. A second limitaton of PM torquers is the inefficiency of such torquers, particularly in terms of the torque per unit volume provided by the conventional arrangements. The requirement that the permanent magnet be located on the wheel or rotor, results in a greater wheel mass and consequently more power required to torque the wheel for desired corrections.
An alternative prior approach employs a conventional current feedback coil drive in a solenoid torquer configuration. This approach readily provides an improvement of better than order of magnitude in torquing efficiency compared with the permanent magnet torquer. In addition, the cost of the solenoid torquer configuration is significantly less than that of the permanent magnet torquer. The efficiency factor improvement is readily apparent from the relation between gyro drift and torque disturbance. Such drift is proportional to a disturbance torque divided by the angular momentum of the system. Thus, for a given disturbance torque, a larger angular momentum results in a lower drift value. The solenoid torquer permits operation with greater angular momentum for a given torquer size than a permanent magnet torquer, and thus a given disturbance torque results in less drift which requires correction. Furthermore, in an aircraft environment, the larger torque capacity of solenoid torquers provides the ability to balance larger inertial reaction forces. In spite of these advantages over PM torquers, conventional solenoid torquers are severely limited in performance due to problems such as nonlinearity, asymmetry, hysteresis and scale factor instability.
Accordingly, it is an object of the present invention to provide an improved solenoid torquer having precise and efficient high force level torquing.